In a surprise, Secretary of State John F. Kerry announces that he'll host Israeli and Palestinian envoys in Washington as early as next week.

JERUSALEM — In a surprise announcement, U.S. Secretary of State John F. Kerry said Friday night that he would host Israeli and Palestinian negotiators in Washington as early as next week in a possible renewal of long-stalled peace talks.

But Kerry's declaration seemed to catch both Israelis and Palestinians off guard. Neither side has yet publicly embraced Kerry's proposal for restarting talks and both have expressed reservations.

Skeptics said that Kerry's pressure might bring the parties together in the same room but that chances for success would be slim if either side was a reluctant participant.

U.S. officials, who had said for two days that they did not expect to announce a resumption of talks, said the two sides had narrowed their differences by Friday afternoon.

"They have agreed on core elements that will allow direct talks to move forward," said a senior State Department official, who was not authorized to speak publicly and therefore requested anonymity.

No Israelis or Palestinians were present during Kerry's news conference in Amman, Jordan. A spokesman for Israeli Prime Minister Benjamin Netanyahu said he had no immediate comment.

Nabil abu Rudaineh, spokesman for Palestinian Authority President Mahmoud Abbas, issued a statement acknowledging that "progress was made which brought agreement on the principles that allow resumption of negotiations."

But other Palestinian officials cautioned that it was premature to say direct negotiations had resumed and that final details of Kerry's framework must still be worked out.

"There is progress, but the issues of difference are not yet resolved," said Wasel abu Yousef, a member of the Palestine Liberation Organization executive committee.

Palestinians still say Kerry's plan does not go far enough in forcing Israel to accept as a basis of talks the borders that existed before it seized additional territory in the 1967 Middle East War.

But despite Kerry's flurry of phone calls with Israelis and Palestinians on Friday, and a brief helicopter visit to the West Bank, he was unable to get Israel to accept the condition or persuade Palestinians to back down, Yousef said.

Palestinians' lackluster support was evident during a Ramallah photo op Friday with a smiling Kerry and somber Abbas. "Mr. President, you should look happy," Kerry said. Abbas did not respond.

"The whole situation is still on hold and we still need clarifications from Netanyahu," Yousef said, adding that Palestinians decided to send representatives to Washington next week as "a diplomatic way of not describing Kerry's efforts as failure."

Netanyahu has steadfastly refused to endorse the 1967 lines as a basis for border talks, and some members of his coalition government threatened to quit if he does. When a report surfaced Thursday that he had agreed to such terms, his office quickly denied it.

Kerry has not released the terms of his proposal. Among other things, it is expected to contain confidence-building measures for the Palestinians, including the release of prisoners held by Israel, restrictions on settlement construction in the West Bank and economic investment.

In his brief remarks Friday night, Kerry cautioned that the agreement was still being formalized and that revealing specifics might put it at risk.

"This is a significant and welcome step forward," Kerry said.

U.S. officials said the first meeting in Washington would include chief Palestinian negotiator Saeb Erekat, Israeli Justice Minister Tzipi Livni and Israeli negotiator Yitzhak Molcho.

Livni, a leader of Israel's negotiating team, praised Kerry for pressing the sides to get back together.

"Years of diplomatic stalemate are about to end," she wrote on her Facebook page. "The determination of Secretary of State John Kerry, not to be taken for granted, led to the Palestinians and us entering the negotiating room."

But others said prospects for success were dim, particularly given the pessimism of Palestinians.

"If Palestinians are saying they were pushed into this, that's not a good sign," said an Israeli government official who requested anonymity because he was not authorized to speak publicly. "It means they might look for the first excuse to jump out of the talks."

It remains unclear which issues could be discussed next week or when Netanyahu and Abbas might join the process.